Neutrophils (PMNs) are an essential component of the host defense in periodontal disease and other bacterial infections. PMN function is modulated by ligand binding to surface receptors, an event which gener- ates phosphoinositide hydrolysis products and transient increases in cytosolic Ca2+. These intracellular signals cooperate with each other to mobilize protein kinase C (PKC) and initiate many essential PMN activi- ties. Recent evidence suggests that Ca2+ signalling is significantly altered by polyamines, which are prevalent in the gingival fluid of inflamed periodontal pockets. Based on this evidence, we hypothesize that gingival fluid polyamines can significantly prolong the duration of both receptor-operated Ca2+ mobilization and_Ca2+-dependent-PKC mobiliza- tion, and thereby modulate many important Ca2+- and PKC-dependent PMN responses to extracellular stimuli. The studies detailed in this propos- al will test this hypothesis in vitro, using PMNs and HL-60 cells stimu- lated with fMLP, C5a, and LTB4 to examine the effects of polyamines at three levels of action: 1) Modulation of the kinetics of chemoattractant-induced Ca2+ mobiliza- tion. The mechanism of these effects will be examined by assessing polyamine effects on phosphoinositide metabolism and on the functions of Ca2+ channels, plasma membrane Ca2+-ATPases, and calciosomes. 2) Modulation of PKC translocation, activation and phosphorylation of cell protein substrates. 3) Modulation of Ca2+ - and PKC-dependent cell activities, including superoxide production, secretion, actin polymerization, regulation of intracellular PH, and expression of chemoattractant receptors. Study of this novel aspect of host defense modulation will provide a better understanding of the complex mechanisms involved in the pathogene- sis and progression of periodontal disease. Since polyamine levels are increased in exudates from other inflamed tissues, these studies are relevant to host defense modulation in other types of inflammatory dis- ease.